Alloy of high density



Patented Dec. 20, 1949 UNITED T1 S ALLOY OF HIGH DENSITY Jacob Kurtz,Teaneck, and Harold G. Williams, Ramsey, N. J., assignors toCallite'Tungsten Corporation, Union City, N. J., a. corporationofDelaware No Drawing. Application September 30, 1942, Serial No. 460,226

1 Claim.

'1 The present invention relates to alloys of refractory metals such astungsten, molybdenum, rhenium, and tantalum. More particularly, it

, relates to alloys of such metals that are of high density and freefrom the usual porosity and intergranular voids that are characteristicof alloys time that the article is strong enough to be handled forfurther treatment. Further treating and sintering at temperaures equalto approximately 90% of the fusing current for the particular rod oringot, further shrinks and strengthens the rod or ingot. The treatedingot, however, is still quite porous and has many intergranular voids,the density at this stage being approximately 17-18 grams per cubiccentimeter in the cast of tungsten.

The rod or ingot must then be hot swaged until it is further compactedwhereby the density increases rapidly from the values of 17-18 to avalue approximately 19.3 for fully swaged rods, having a reduction inarea of 80-90%. This density is generally referred to as the theoreticaldensity.

According to the method of the present invention, purified refractorymetal powder, such as tungsten or molybdenum, having a particle size ofapproximately from 1 to .25 microns, is combined with a small buteffective amount of powdered metals that result in the alloying, bondingand densifying of the rod or ingot without the necessity of swaging.These alloying metals are formed from an appropriate selection of afirst group of metals that are more properly described as alloyingmetals, and a second group that perform the function of refining thegrain structure so as to permit control of grain growth, and a thirdgroup consisting of the noble metals. In the first group are manganese,iron, cobalt and nickel; the second group consists of beryllium,zirconium, chromium, vanadium, titanium and uranium; and the third groupconsists of platinum, palladium, gold, osmium, iridium, ruthenium andrhodium.

This alloying, bonding and densifying metal consists of a mixture offinely divided'metal'powders approximately one-half by weight of basemetal and the balance noble metal. After these two constituents arethoroughly mixed they are added to the refractory metal powder in theproportion of approximately .25%-4% by weight, thoroughly ball-milledand mixed to assure uniform distribution of the densifying metalthroughout the refractory metal. The mixture is then ready for pressinginto formed pieces, discs, and the like, and subsequent heat treatmentat a temperature of 1500-2000 C. in a hydrogen or neutral atmosphere oreven in a high frequency vacuum furnace, using a molybdenum or tung stentube or elongated crucible.

Where the term refractory metal is used in this specification it isintended to denote metals not easily fusible and Whichhave meltingpoints as high as, or'higher than, 2500 C., and more particularly, themetals tungsten, molybdenum and tantalum.

The following'two examples are given, the first being without a metal ofthe second group, and the second containing such a metal:

Example I First, the alloying, bonding and densifying metal mixture isprepared. Approximately equal portions by weight of pure finely dividednickel powder, and pure finely divided platinum powder are thoroughlymixed and ball-milled. Platinized nickel powder (containingapproximately 50% by weight of'platinum) made by shaking nickel powoftungsten powder.

This mixture is then ready for pressing in a suitable mold either in atablet machine, or in a conventional hydraulic press, depending on thesize and shaped the desired finished piece. After pressing, the formedpieces are then heat treated in an electric furnace at a temperature of1500-1850 C. in a dry hydrogen atmosphere for about one hour, the timedepending, of course, on the size, shape and number of pieces insertedinto the hot zone, and the characteristics of the furnace.

After this heat treatment, the pieces have been fully sintered andshrunk in volume in a uniform .in the same manner as in Example 1.

manner maintaining in a characteristic way all the sharp contours of thepieces. The volume shrinkage will vary from about 15-25% of the originalvolume depending on pressures and sintering temperatures used. With 4%Ni and /4% Pt 99.5% tungsten, densities are obtained without swaging ashigh as 19.35 grams per cubic centimeter, comparable to the density of apiece of hot swaged tungsten rod of 19.3.

This high density is an indication of a fully sintered bodyexceptionally free from porosity and intergranular voids. Themicro-structure confirms this, and shows a well ordered, well developed,fairly large grained crystal structure.

Example II The alloying, bonding and densifying metal mixture isprepared. Approximately equal proportions by weight of finely dividednickel beryllium powder and pure finely divided platinum powder arethoroughly mixed and ball-milled. Then approximately 1% by weight ofthis prepared mixture is added to finely divided tungsten powder of aparticle size of 1-25 microns, and is thoroughly mixed. It may beball-milled for a period of several hours or at least long enough toinsure the uniform distribution of the small amount of alloying powdersthroughout the mass of tungsten powder.

This mixture is then pressed in a mold and heat treated in an electricfurnace at a temperature of 1500-1800 C. in a dry hydrogen atmosphere Inthis method the grain size and structure may be controlled by ng theproportions of the alloyfr" ing, bonding and densifying metal between25% to 4% by weight. Somewhat more than 4% may be added but little ifany advan age is secured thereby. As in Example I, densities areobtained without swaging higher than 19.35 grams per cubic centimeter,comparable to the density of a piece of hot fully swaged tungsten rod of19.3. The grain structure may vary from quite small grains to very largegrains in accordance with the amount of the alloying metals that havebeen added.

An alternate method of adding the nickel and platinum in Example I maybe employed with equally satisfactory results. Standard stock solutionsof the soluble salts or compounds, or the metals to be added, are madeup. The salts chosen belong to the class which when completelydehydrated are easily decomposable to their metallic states When heatedin a reducing atmosphere. rides, and nitrates of iron, cobalt, nickeland manganese; chlorplatinic acid, ammonium chlorplatinate, goldchloride, and similar compounds of the other metals used. A measuredamount of the solution of the base metal and the noble metal is added tothe oxide of the refractory metal, thoroughly dried in a manner toassure uniform distribution of the salts, and subsequent ly this mixtureis reduced in the usual manner to metal powder. Or the solutions may beadded to the refractory metal powder forming a slurry, care being takento mix and stir the powder thoroughly to get uniform distribution of themetallic Examples of such are the acetates, chlo- 4 salts added. Theslurry is carefully dried with constant stirring, and, when dry, it issieved to break up any lumpy formation, put into a nickel coat and runthrough a reduction furnace to insure complete reduction to theirmetallic states.

"The powders are then sieved through 200 mesh and are now ready forpressing into any desired form or shape.

The examples given above illustrate an alloying of tungsten with nickeland platinum and tungsten with nickel, beryllium and platinum. However,excellent results may be obtained by substituting for all or part of thenickel, a nickelous alloy of zirconium, chromium, vanadium, titanium oruranium. These nickelous alloys can be made to contain from 10-50% ofthe grain refining metals, beryllium, zirconium, chromium,

vanadium, titanium, uranium. Therefore, the

percentages of these metals can be adjusted to give any desired amountup to 50% of the nickel content.

Additions of beryllium, zirconium, etc., increase the hardness of therefractory metal alloy. Heating at approximately 600-1000 C. for periodsof about l-lO hours will cause precipitation hardening whenever'desired.They also perform the function of grain refining and of effecting auniform grain structure in the finished alloy, thus affording a readymeans of controlling the grain growth.

While the examples given above illustrate the method of making the densealloy of the invention with tungsten as the refractory metal, it will beunderstood that a similar method of alloying molybdenum, rhenium andtantalum also comes within the scope of the invention. In the case ofmolybdenum, however, about 1% of the alloying, bonding and densifyingmetals should be added.

The alloys of the invention are extraordinarily suitable for making theface plates of contact points and may be used for making large shapedobjects such as crucibles and cylinders, both solid and hollow. Theymay, in fact, be used wherever hard, strong, dense metal capable ofwithstanding high temperatures is desired.

Having thus described our invention, what we claim is:

Sintered alloy of high density comprising 99% tungsten, 0.25% nickel,0.25% beryllium, and 0.50% platinum and having a density approximating19.3 grams per cubic centimeter.

JACOB KURTZ. HAROLD G. WILLIAMS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,418,081 Laise May 30, 19221,932,678 Ruben Oct. 31, 1933 2,074,474 Jedele Mar. 23, 1937 2,157,935Hensel et a1 May 9, 1939 2,183,359 smithels Dec. 12, 1939 2,200,088Kelly May 7, 1940 2,227,446 Driggs Jan. 7, 1941

